[MockHardware] Enable disabling of command to simulate HW failures. (backport #1027)

[mergify]

This is an automatic backport of pull request #1027 done by Mergify.
Cherry-pick of bc8052a has failed:

On branch mergify/bp/humble/pr-1027
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Changes to be committed:
	modified:   hardware_interface/include/mock_components/generic_system.hpp
	modified:   hardware_interface/src/mock_components/generic_system.cpp
	modified:   hardware_interface/test/mock_components/test_generic_system.cpp

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   hardware_interface/doc/mock_components_userdoc.rst

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/github/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

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